GB2351141A - Pinch valve - Google Patents

Abstract

A pinch valve is characterised in that its pipe member 2 is made from an extruded cross-linked polyolefin. The valve may be used in the making of water mains. The cross-linked polyolefin is more resistant to stress cracking than previously known materials.

Description

1 2351141 DISTRIBUTION SYSTEM VALVE MEMBER This invention relates to

inhibiting fluid flow, and more particularly to a valve member for temporarily inhibiting the flow of fluid in a distribution main and to a new water distribution system.

Distribution mains, for example, water distribution pipe systems, frequently have the requirement that the flow of fluid needs to be stopped or diverted, for example, when carrying out damage repairs, leakage repairs, relining, mains extension or service connections, or inspection of the system or a part thereof. Commonly metal valves are inserted into the pipe system at discrete locations so that the water supply can be turned off or diverted at that point.

The metal valves currently in use are large and cumbersome, subject to corrosion, particularly when used with buried pipe systems, expensive, and frequently fail in service due to leakage or blockage.

There is a need for an improved method of inhibiting or diverting fluid flow in a water distribution main which is cheaper, does not introduce potentially corrodable moving parts into the pipe system, and can be used by relatively unskilled technicians.

A technique which has been developed and widely applied in the gas industry is that of "squeeze off", in which a clamping device is applied to a polyethylene gas main which locally deforms the main by flattening in order to cut off the gas flow whilst repair or 2 rehabilitation work is carried out. This method works well in practice, but it is well recognised that polyethylene pipes can be squeezed of f in this way only once, since repeated applications of the squeeze off technique very quickly lead to stress cracking of the pipe. This means that each time the squeeze off technique is employed, current regulations demand that a fresh section of pipe must be chosen that can be no closer than 3 to 4 pipe diameters of the original squeeze off point. The requirement to expose a fresh section of pipe can be inconvenient, particularly where buried pipe systems are concerned.

The squeeze off technique has not been used much in the water distribution industry, because the distribution mains used therein, comprising mostly buried earthenware or PVC pipes, are not always suitable. Even if the squeeze off technique were to have been envisaged in the water distribution industry, it would have been considered impracticable for most applications due to the necessity to expose a fresh section of pipe each time the squeeze off clamp is applied. In any event, the present invention is not concerned with casual instances where a pipe might need to be constricted for some unusual reason and where the squeeze off technique finds its most frequent application. The invention is concerned with providing inexpensive simple valves where they are known to be required for normal, if infrequent, operation such as at junctions etc.

The present invention seeks to overcome the problems set out above by inserting into the water distribution system at selected points one or more valve members of 3 cross-linked polyolefin pipe. Crosslinked polyolefin pipe, particularly when produced by peroxide crosslinking, has been found to be resilient and highly resistant to stress cracking. These properties can allow the cross-linked polyolefin pipe to be repeatedly subjected to a squeeze off flow inhibition technique at the same point, which current regulations do not permit for non-cross-linked polyolefin pipe.

According to the present invention, therefore, there is provided a valve member for a fluid distribution system, the member comprising an extruded cross-linked polyolefin pipe of less than three metres in length and having at each end a connector for connection to another valve member or the system, the pipe being adapted to restrict or prevent flow through the pipe by application of an external pressure to the pipe in order resiliently to deform the pipe cross-section.

When the external pressure is released the extruded cross-linked polyolefin pipe substantially returns to its former dimensions and normal fluid flow is resumed.

Whilst the invention is primarily concerned with stopping fluid flow in a distribution main, so that fluid flow is either stopped or diverted, it may be sufficient in certain cases for the flow of fluid to be reduced rather than completely stopped. A particular advantage of the method of the present invention is that fluid flow can be temporarily inhibited or stopped whilst the pipe is full of fluid, and there is no need to drain the system before the pipe can be blocked or stopped.

4 In another aspect, the invention provides a liquid, and especially a water, distribution pipe work system comprising valve members as described above.

The cross-linked polyolefin of the plastics pipe can comprise any suitable homopolymer or copolymer of ethylene, propylene, n-butylene, n-pentene or higher olefin homologues, and can include, if desired minor amounts of other comonomers such as, for example, dienes, vinyl esters and other ethylenically-unsaturated monomers.

The polyolefin of the pipe wall can be cross-linked by such techniques as radiation cross-linking, using a high energy electron beam or by silane cross-linking, using silane monomers which cross-link in the presence of moisture, but preferably the polyolefin material is cross-linked using a peroxide cross-linking method. In the peroxide cross-linking method, a small quantity of a heat activatable peroxide, for example, di-tert-butyl peroxide (DTBP), is incorporated into the polymer granules and fed into the barrel of an extruder. At the melt temperature of the polymer material, the peroxide breaks down forming free radicals which cross-link the polymer chains as the extruded polymer material leaves the extruder die. Peroxide cross-linked polyolefins are particularly resistant to stress cracking and also give greatly improved resiliency, so that a pipe formed from a peroxide cross-linked extruded polyolefin can be repeatedly subjected to a squeeze off method at the same point without substantially weakening the pipe at that point.

Preferably the length of extruded cross-linked polyolefin pipe is connected to the fluid distribution system by the use of fusion fittings, and more preferably by the use of electrofusion fittings. It has been found that the shorter the length of a pipe between two such fittings, the greater the apparent pipe strength. Preferably the length of cross-linked polyolefin pipe used is from 2 to 10 times the diameter of the pipe, more preferably from 4 to 8 times, for example around 6 times the diameter of the pipe. Pipe diameters for water distribution mains generally vary from 63 to 315 mms.

The apparent improvement in strength obtain from using a relatively short length of cross-linked polyolefin pipe supported by electrofusion fittings can allow a thinner walled pipe to be specified to ease squeeze off and speed recovery rates, or can allow the use of lower density polyolefin material to provide increased flexibility for squeeze off operations.

Preferably the cross-linked polyolefin pipe has a wall thickness of from 2 to 30 mms.

It is particularly preferred to use as the extruded cross-linked polyolefin a polyethylene which results in an MRS classification of between 8 and 12.5. (MRS classification can be determined in accordance with ISO 1167, ISO 12162 and ISO TR 9080 (ISO 1167;1996. Plastic pipes for the transport of fluids - Determination of the resistance to internal pressure; ISO 12162;1996:

Thermoplastics materials for pipes and fittings for pressure applications - Classification and designation; ISO TR 9080;1992: The determination of the long term hydrostatic strength for thermoplastics pipes materials).

6 The most relevant document is in fact ISO TR 9080 which is accepted conventionally for judging and ranking thermoplastics pipe materials.) In certain circumstances it can be desirable to coat the extruded cross-linked polyolefin material with an external polymeric film. EVOH films can be applied, for example, to form gas barriers to prevent permeation of air into the water system. In a similar manner, a coloured film can be applied which, for example, can highlight the centre of the pipe section, thus indicating to the technician the optimum point for the application of the squeeze off clamping tool.

Any suitable clamping device can be used in order to apply the localised external pressure to the pipe wall in order to resiliently deform the pipe cross section. The device can clamp the pipe in a horizontal plane or a vertical plane, although where buried pipes are concerned, clamping in a vertical plane is usually preferred. The clamping tool can be manually operated or hydraulically driven.

A feature of the invention is that the external pressure can be applied repeatedly to the same section of pipe wall without significantly degrading the physical properties of the cross- linked polyolefin pipe.

Valve members are preferably supplied as prefabricated assemblies from the factory so that they are suitable for connection into water distribution systems, for example, at street junctions, where it is current practice to install a number of valves on site.

7 Thus one connector can comprise a tee piece to which one end of the pipes of two other members as def ined above are also connected. The assembly will have been welded within the factory environment and as such it is possible to ensure consistent quality of the joints. A connector, preferably an electrofusion coupler, is thus at each end of the three branches of the complete valve member assembly.

In practice, the flow stopping operation is a very simple matter. A distribution team can carry a squeeze off clamping off tool and if a flow stop is required they can access the buried prefabricated assembly and apply the tool to the middle of the appropriate pipe section.

is After the desired work has been carried out, the clamping tool can be released and the pipe resiliently recovers to its former diameter, permitting renewed fluid flow.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows an end elevation of a section of a cross-linked polyolefin pipe with a squeeze off clamping device disposed thereabout; and Figure 2 shows a valve member in accordance with the present invention.

Referring to Figure 1, a clamping device illustrated generally at 1 is disposed about a cross-linked polyolef in pipe 2 the clamping device comprises a f ixed jaw 3 mounted on legs 4 and a slidable jaw 5 which can move in a vertical plane and is also mounted on the legs 8 4 a frame member 6 spans the upper ends of the legs 4 and is rigidly attached thereto. Frame member 6 has a central screw threaded aperture 7 within which is situated a screw threaded thrust bar 8, having at its upper end a hand-operable cross piece 9. The thrust bar 8 can be turned by hand using the cross piece 9 and engages at its lower end 10 with the slidable jaw 5 of the clamping device 1.

In use, the clamping device 1 is positioned on the cross-linked polyolefin pipe 2 and cross piece 9 turned by hand until the thrust bar 8 forces the slidable jaw 5 into contact with the cross-linked polyolefin pipe 2. Further turning of the cross piece 9 squeezes the cross- linked polyethylene pipe 2 between the Jaws 3 and 5, flattening the cross section and blocking the flow of fluid through the pipe. Depth stops 11 are rotatable in the legs 4 and prevent the over- compression of the pipe 2. Generally, pipe compression Ue the final distance between jaws 3 and 5) is limited to not less than 80% of twice the wall thickness, and not less than 90% in the case of pipe diameters greater than 250mm.

When it is desired to restore fluid flow, it is 25 merely necessary to loosen the clamping device 1, whereupon the cross-linked polyethylene pipe will resiliently recover to its former shape. The operation can be repeated several times without endangering the integrity of the crosslinked polyolefin pipe.

Figure 2 shows a valve member assembly 20 according to the present invention. The term "valve member" rather than "valve" is used herein because a separate squeeze 9 of f tool 1 is required to create an actuatable valve.

The assembly 20 of Figure 2 comprises three valve members 22,24,26, each sharing a common tee piece connector 28 at one end. At each other end of each member is disposed an electrofusion coupler 32,34,36.

Electrofusion coupling to cross-linked polyolefin pipe is possible, but there is a degree of prejudice, largely unfounded, that such coupling is difficult. This is based on the fact that cross-linked polyethylene does not liquefy when heated and therefore does not, on the face of it, fuse and weld in the same way as uncross linked polyethylene. An advantage of the present invention is that these perceptions can be overcome by performing the electrofusion to cross-linked polyethylene in the factory and supplying the assembly as a complete unit. of course, such an assembly would not be necessary where the entire pipe distribution system was cross linked polyethylene, but that will not usually be the case, given the expense of cross-linking. Where the system is uncross-linked polyethylene, then the assembly poses no different issues to an ordinary tee piece coupler, other than a larger trench being required. In other words, each coupler 32,34,36 can be connected to the usual uncross-linked polyethylene pipe of the water distribution system without any more difficulty or concern than any other junction or joint in the system.

Indeed, in this respect, the couplers 32,34,36 could even be provided with heating elements which are quite separate from the heating mechanism employed to connect the couplers to there respective valve member 22,24,26 so that the bond therebetween is not disturbed when the coupler is connected to the distribution system.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (13)

1 A valve member for a fluid distribution system, the member comprising an extruded cross-linked polyolefin pipe of less than three metres in length and having at each end a connector for connection to another valve member or the system, the pipe being adapted to restrict or prevent flow through the pipe by application of an external pressure to the pipe in order resiliently to 10 deform the pipe cross-section.

2. A member according to claim 1 wherein the fluid distribution main is a water main, and said member is adapted for mains water transport.

3. A member according to claim 1 or 2 wherein the cross-linked polyolefin is cross-linked polyethylene.

4. A member according to claim 3 wherein the 20 polyethylene has an MRS classification of from 8 to 12.5 MPa.

5. A member according to any of the preceding claims, wherein the polyolefin is cross-linked by a peroxide 25 cross-linking method.

6. A member according to any of the preceding claims, wherein the connector comprises an electrofusion fitting.

7. A member according to any of the preceding claims, wherein the length of the cross-linked polyolefin pipe used is from 2 to 10 times its diameter.

12 A member according to any of the preceding claims, wherein the extruded cross-linked polyolefin pipe has a wall thickness of from 2mm to 30mm.

9. A member according to any of the preceding claims, wherein the extruded cross-linked polyolefin pipe is coated with an external polymeric film.

10. A member according to any of the preceding claims, further comprising a clamping device to apply said localised external pressure.

11. A member as claimed in any preceding claim wherein one connector comprises a tee piece to which one end of is the pipes of two other members as claimed in any preceding claim are also connected.

12. A water distribution pipe work system comprising valve members as claimed in any preceding claim.

13. A valve member substantially as hereinbefore described with reference to and/or as illustrated in the accompanying drawing.